Background

• NMFC “Backplane” gathering mainly inertial data

• “Grim Reefer” gathering some inertial, mainly high-speed analog data

• “POTATO” gathering high-speed analog data

Measurement storage schema

• Bin measurements by rate

• Highest frequency grouped into several measurements

• 24 bits requires us to define our own endianness, error-prone

• Microsecond accuracy reasonable

• Down-convert inertial measurements to 16 bit ints because that’s how they start

  • Fundamentally, 32 bits of precision is too many for 16 bits of information

• Store only one of the several temperature readings

Events of interest

• Everyone detects boost, because we can’t store all the high-frequency measurements

• Everyone detects landing, to save power and have less garbage at the end

• Grim and Potato need to capture before and after apogee, to get load measurements

Detection options

Boost

• Acceleration

  • Not affected by venting or wind

  • Potentially affected by bumping, but powered on at the pad

• Altitude

  • Less reliable than acceleration due to venting issues

    • May be overblown

    • Testable

  •  

• RRC3s capable of live serial output

  • Reliable because of COTS

  • Adds complexity to code

  • Adds complexity to wiring harness

Choice:

For all, OR gated:

• 5 gees for 0.25s

  • Magnitude

    • Insensitive to orientation changes

    • Insensitive to programming errors

  • 5 half (arb) of expected g

  • 0.25s worked for SCRAP

• Altitude reaches 500 ft above ground level in less than 3s

  • 500ft common arming alititude for altimeters

  • 3s double (arb) of simulated 1.6s

Pre-Apogee

• Timer after boost

• Timer after burnout

  • Slightly less simple

• Altitude slowly changing

Choice, for Backplane:

• After boost, <50 fps gives 2 (arb) seconds leading up

Choice, for Grim:

• Not needed, enough data rate

Choice, for POTATO:

• After boost, <50 fps gives 2 (arb) seconds leading up

• OR backplane detecting pre-apogee

Apogee

• Not specifically helpful during the flight

Main

• Pure timer

• Altitude on the way down

Choice, for Backplane:

• Main + 500ft (arb)

Choice, for Grim:

• Not needed, enough data rate

Landing

• Timer

• Acceleration

• Altitude

Choice, for all:

• Timer is the simplest, no loss to over-timing

Final CONOPS

Backplane

• Stores a 3s rolling buffer

• Detects boost OR gated measurements

  • 5g 0.25s

  • >500ft <3s

• Detects 3s before apogee

  • <50 fps vertical velocity

• Detects 10s before main

  • 500 ft above main

• Detects landing by 400s timer

Grim Reefer

• Stores a 3s rolling buffer

• Detects boost OR gated measurements

  • 5g 0.25s

  • >500ft <3s

• Detect landing via 400s timer

POTATO

• Stores a 3s rolling buffer

• Detects boost OR gated measurements

  • Sensor module command

  • Own altimeter 500ft <3s

• Detects 3s before apogee

  • Sensor module command

  • <50 fps vertical velocity

• Detects 10s before main OR gated

  • Sensor module command

  • 500 ft above main

• Detects landing by 400s timer

To do